Lightning arrester



July 10, 1934. F. scHROTER LIGHTNING ARRESTER Filed Sept. 10, '.1929

INVEHTOR .Tr-Hz Schrrer H TTORNE Y Patented July 10, 1934 UNITED STATES LIGHTNING ARBE STER Fritz Schriiter, Berlin-Schmargendorf, Germany,

assignor of one-half to Radio Patents Corporation, New York, N. Y.

Application September 10, 1929, Serial No. 391,644

2 Claims.

This application refers to electric protective apparatus usually known as lightning arresters and used in electrical systems to prevent such excessive rises of electro-motive forces as might g damage the installation of the lines or the apparatus connected to the lines. The general term of lightning arrester? has been applied to abnormal rises oi voltages no matter what their causes, and the object of such lightning arresters consists of i guarding against any abnormal rise of voltage in an electrical system.

This application in particular, relates to such rises of voltage which occur very rapidly and have very short duration, such as occurs especially in the case of lightning striking an electric line whereby a rapid disturbance in the form of a so-called traveling wave or surge is transmitted along the line. Therefore, a device intended to discharge the excess energy occurring during such disturbance, must possess on the one hand, the property of presenting high resistance so as to prevent a discharge under normal conditions, and on the other hand, it must practically instataneously decrease this resistance so as to present at once a discharge path for the excess energy during the short interval of its existance. It is an object of my invention to provide a successful lightning arrester which relieves the system immediately of excess energy due to rises in potential.

A further object of my invention is to provide means in connection with a lightning arrester by which the normally high resistance of the discharge gap of the arrester is immediately lowered to effect an immediate discharge of excess energy due to rise in potential.

Another object of my invention consists in providing a lightning arrester, the resistance of which decreases as the amount of energy to be discharged increases so as to secure an immediate and rapid discharge of excess energy to ground due to a rapid surge occurring upon the line.

Still a further object of my invention is to provide means in connection with a gaseous discharge arresting gap which enables it to secure an immediate response of the gap at rapidly occurring rises of voltage.

Another object of my invention consists of pro- The other objects of my invention, not at this time particularly enumerated, will be clearly understood from the following detailed description of my said invention, but I want it to be understood that the following disclosure is illustrative 60, only of the nature of the invention and that I may vary the construction actually shown to the full extent which is consistent with the broad meaning of the terms in which the appended claims are expressed.

Figure 1 of the drawing shows one form of a lightning arrester in which my invention is embodied.

Figure 2 is a graph intended to explain the theoretical phenomenon occurring in a lightning arrester in accordance with my invention.

Figure 3 is another example of a lightning arrester in accordance with my invention in a modified form as compared to Figure 1.

Figure 4 illustrates a. further modification of a discharge lightning arrester in accordance with my invention.

Figure 5 represents a modification oi. the arrester as described by Figure 4.

Similar reference numbers designate similar elements throughout the different views of the drawing.

With the various objects of the present invention in view, the said invention consists primarily in a lightning arrester comprising a gas-filled vessel or envelope preferably of pyrex glass or quartz to withstand high temperature and mechanical stress and which contains main electrodes tobe connected between a point on a transmission line near to an electrical apparatus to be protected from excess voltage, and ground. The size and dimensions of the vessel or envelope and the arrangement and spacing of the electrodes is such as to provide a gaseous path with normally suflicient resistance to withstand the usual operating voltage on the system occurring under normal conditions. As soon as an excess voltage is established upon the electrical system or line, the gaseous space between the electrodes will become conductive on account of ionization of the gas molecules and will then serve as a bypass for excess energy.

As is well known in electrical theory of discharge devices, it requires some time for a sufficient number of gas molecules to become ionized, and it is therefore apparent that an arrester of this kind, although it may be quite effective for low frequency or slowly occurring disturbances, will be too sluggish to immediately respond when a quick acting surge or disturbance occurs, such as is mused for instance when lightning strikes a line or also when a lightning discharge takes 1 lac; in the immediate neighborhood of such line. In order to overcome this disadvantage and to make such lightning arrester of the gaseous type adapted for the very rapidly acting and in practice, most dangerous kind of disturbances or surges which are sometimes termed high frequency surges, I provide a third electrode arranged to act indirectly on the gaseous discharge and adapted to pre-ionize the discharge to an extent as to enable its immediate and instantaneous breakdown by the excess voltage occurring upon the line.

For this purpose, the auxiliary electrode, in accordance with my invention, is connected to that point of the network at which the excess voltage is established, that is, in the example above referred to, to the line or also to the point of the net work system to which the excess energy is to be dissipated; that is, to ground in the ordinary cases.

Referring to Figure 1 of the drawing, an arresting tube in accordance with my invention is shown in its simplest embodiment.

Numeral 1 represents a vessel consisting of insulating material, preferably of pyrex glass or quartz and of oblong shape with a restricted portion in its middle as shown. At the opposite ends of this vessel, two electrodes 2 and 3 which may be of any well-known type and consist of metal or combination of metals in accordance with the known art, are sealed into the tube with electrode leads 4 and 5 extending to the outside for connecting the arrester between points of the network to be protected against excess voltage. Thus, for instance, the lead 5 in the example chosen is connected to ground as at 5 and the lead 5 in the example chosen is connected to a point of an electric line 4 such as for instance, a point in the neighborhood of the electrical apparatus" which should be guarded against injurious effect of rapid disturbances occurring at this point of the line or transmitted to this point from some other point. The vessel is filled with a gas of suitable nature and condition.

Preferably, a rare or inert gas such as for example, a mixture of helium and neon at a pressure of from 0.1 millimeter to 0.5 millimeters of mercury is used. However, it is to be understood that the choice of the nature and condition of the gas or mixture of gases used has to be made with the purpose of providing a gaseous atmosphere which at normal electrical conditions of the network prevents a high resistance and which, with abnormal conditions such as with excess voltage occurring, is able to change its resistance rapidly by the action of ionization effected by the special instruments and arrangement of my lightning arrester.

I have found that the most favorable results are obtained when an arresting gap of this kind is filled with an inert gas such as neon under very low pressure, whereby the time of ignition is furthermore decreased by using for instance, a pressure of 0.2 to 0.1 millimeter of mercury and the break-down potential between the inner electrodes 2 and 3 becomes relatively high.

In accordance with my invention, I provide a further third or auxiliary electrode 6 in the form of a metallic layer or cylinder closely surrounding the restricted portion of the tube. This auxiliary electrode is directly connected to the terminal or lead 5, which may be connected to the point at which the excess voltage occurs, that is,

in the usual arrangement, to the network line or to the point of the net work to which the excess energy is to be dissipated; that is, ordinarily to ground such as has been illustrated in the drawmg.

This alternative connection or the auxiliary electrode to either one or the other of the main electrodes is possible in view of the fact that the current to be carried by the auxiliary electrode is a capacitative displacement current. The connection of the auxiliary electrode 6 to the line terminal 5 is made through a lead 8 connected to a metallic ring 7 shrunk on the electrode 6. It is understood that this connection of electrodes 5 and 6 may be carried out in any other suitable manner and may, for instance, be made within the tube itself. This outside electrode 6 forms together with the wall of the vessel and the gaseous ions, an electrical condenser. The capacitative current flowing in and out of this condenser is suflicient to ionize or pre-ionize the entire volume of the gas between the inner electrodes and to thus instantly prepare the break-down of the arresting gap. Thus, as soon as the voltage on the line assumes an excessive increase, the ionization within the entire gaseous spaces will start immediately provided that a suitable pressure and distance of the upper end a of the auxiliary electrode 6 from the inner electrode 2 has been chosen.

In Figure 2, a theoretical curve is shown which is intended to elucidate more clearly the operation of the new device. The curve shown represents the change of the electric current i established within the discharge gap as ordinate depending on the voltage 1' applied as abscissa. With the voltage applied to the gap increasing from zero, the discharge current varies gradually along an almost straight line until very soon, a point p is reached at which the current jumps abruptly to a very high value proportionately much higher as shown in the figure. The range from o to p is known as the pro-glow state of the tube and is due to the ionizing action of initial electrons always present within the gas which, under the influence of the electric field, attain sufiicient velocity to dislodge further electrons from the gaseous molecules and thus increases the current. Thus, further electrons and ions are produced which again, under the influence of the electric field, will take part in the ionization of the remaining molecules so that a cumulative ionization effect takes place. This increase of ionization is at first gradual until by the cumulative effect at point p, such a degree of ionization is reached that an abrupt current rush, such as is shown in the figure takes place. It is the function of the auxiliary electrode 6 to produce such a state of pro-ionization or pre-glow within the range 0 and p that with a voltage rise occuring on the line, an instantaneous break-down of the gap takes place. By properly designing the auxiliary electrode and its distance from the main electrodes, a specific zero point within the range 0 to p may be adjusted in respect to the amount of the excess voltage at which it is desired to have the gap break down.

Figure 3 shows a tube similar to that shown in Figure 1, the only difference being that the auxiliary electrode is divided into two parts 6' and 6" and connected with the main electrodes 2 and 3 respectively by means of connecting rings '7' and 7" and leads 8' and 8".

In practice, a large number of arresters of the kind described may be made up in a series and mounted in standard size units to be connected by providing a helical discharge path through a tubular helix of insulating material such as pyrex glass. between the discharge electrodes 2 and 3.

The third or auxiliary electrode is formed by a conducting material such as a liquid or a powder closely surrounding the helix.

Referring to Figure 4, 9 represents the tubular helix, sealed to the main envelope or vessel 1 by funnel-like extensions as at 9' so that the entire lightning arrester consists of two independent compartments, one filled with gas for carrying the discharge and a second one filled with a conducting medium such as a salt solution 10 closely surrounding the helical discharge tube. This outside electrode formed by the conducting salt solution 10 surrounds the inner electrode to a variable height. 11 is a metal ring constituting a further electrode arranged on the outside of the outer envelope 1 whereby this ring 11 together with the wall of the envelope and with the salt solution constitutes an electrical condenser which is connected in series with a further condenser formed by the salt solution, the helical tube 9 and the gaseous current carriers within. 12 is an extension on the outside envelope for introducing the necessary amount of conductive salt solution such as for instance of sodium chloride (table salt) to a variable height h. 13 is a further extension which serves to introduce such further constituents into the gaseous atmosphere which are adapted to improve the action as desired. It has been found that potassium gives favorable results in this respect and may be introduced in the gaseous atmosphere of the tube by means of a piece of potassium 14 placed in the extension 13 and heated by a heater 15 after which, the extension 13 is sealed oil from the tube. Instead of using an outside metal ring 11 for applying the electric charge to the inside is connected by the lead 8 to the respective main of the tube, the electric current may be applied, directly to the salt solution 10 by means of an electrode 16 which is sealed into the wall of the outside envelope as shown in Figure 5 and which electrode or the device.

Arresting tubes of the type in accordance with Figures 4 and 5 have to be used in a vertical position. When using an outside metal ring as shown by Figure 4, the variation of the height h of the salt solution has no great influence upon the capacitative current flowing through the gas during normal conditions. With a direct connection of the voltage to the salt solution however, this infiuence becomes larger. It is preferable to put a layer of oil above the salt solution on order to prevent disturbances caused by condensation of water at the upper portions of the inner tube. It is furthermore suggested, in accordance with my invention, to stiffen the salt solution by the addition of a gelatin or the like. Furthermore, it is not absolutely necessary to use a liquid surrounding the helical inner tube. A metal powder or similar medium such as fine iron powder or graphite dust may be used to obtain, satisfactory results.

I have illustrated my invention by certain specific embodiments, but it is to be understood that these are presented for purposes of illustration only and are not to be accorded any interpretation having the effect of limiting the following claims, short of the true and most comprehensive scope of my invention in the art.

Whatis claimed is,

l. A surge protection device for electrical networks comprising in combination a helical tube of insulating material having end chambers and including a gas at reduced pressure, main electrodes disposed in said chambers to form a discharge path through said tube, outside leads from said electrodes for connecting said tube between an endangered point in a network and ground,

a further chamber of insulating material surrounding said tube an electrically conducting liquid in said last mentioned chamber, a further electrode closely surrounding said second chamber, and means for conductively connecting said further electrode to one of said main electrodes.

2. A protection device as claimed in claim 1 in which said second chamber is integral with said helical tube and said liquid is a salt solution.

FRITZ SCHROTER. 

